Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240126

826 PM CDT Sat Aug 23 2014

Issued at 825 PM CDT Sat Aug 23 2014

TSRA triggered off a boundary in Fayette and Marion counties in IL
have since moved off to the east. However, another outflow from
the MCS in IN and KY is edging into Fayette and Marion counties
and may trigger a renewal of TSRA and thus have kept in some small
PoPs until later this evening. Otherwise, a warm and dry night is
on tap with persistence tough to beat for min temp forecast.



.SHORT TERM:  (Through Late Tonight)
Issued at 315 PM CDT Sat Aug 23 2014

I have introduced some slight chance pops into the forecast this
evening across the far eastern portion of the CWA. There is some
weak convergence in this region owing to an old outflow boundary
and SBCAPE is pretty extreme at 6000+ J/KG with little CIN. If
indeed a storm does fire then we might see a pulse severe mode.
Also added some slight chance pops to the eastern Ozarks due to
recent development, however CAPE is much less. As the evening
progresses the surface boundary/front re-establishes itself from
western Iowa southeast along the MS River. The vast majority of
the guidance suggests that any additional precipitation threat
will be elevated and well north of the aforementioned boundary and
outside of our CWA. Min temperatures tonight be a few degrees
cooler in the western CWA owing to lower surface dew points but
comparible to this morning elsewhere.


.LONG TERM:  (Sunday through Next Saturday)
Issued at 315 PM CDT Sat Aug 23 2014

Overall not many significant changes in order through Tuesday with
excessive heat continuing. The upper level ridge remains the
dominant weather feature as it expands to the east and southwest.
The heat advisories and excessive heat warning remain intact
through Monday with no changes. If the ensuing model runs continue
current trends then they will likely need to be extended into

There are some subtle features such as dew points that could mess
with the heat index values and these are the biggest unknowns -
i.e. like today dew points pooling in the mid-upper 70s east of
the river and HI values of 110+. Drier air made a little more
inroads from the Plains into central and southeast Missouri today
and this slight eastward progression into eastern MO is forecast.
Along and east of the MS river the surface boundary is forecast to
waver and surface dew points look to remain a bit higher. If they
remain as high as today then some eastward expansion of the heat
warning may be warranted.

The threat of diurnal convection is expect to increase on Tuesday
but a lack of focus should keep coverage isolated. Finally it
appears we will see a pattern change from the middle into the
later part of the week ahead breaking the heat wave. A positively
tilted upper trof is forecast to migrate from the Great Basin
region late Tuesday and into the Nation`s midsection late Wednesday-
Thursday, lingering into late Friday. This should gradually bring
a cold front into the area with cooler temperatures and increased
threat of scattered showers and thunderstorms.



.AVIATION:  (For the 00z TAFs through 00z Sunday Evening)
Issued at 634 PM CDT Sat Aug 23 2014

Expect VFR flight conditions and light/variable wind to prevail
this evening. There are some isolated thunderstorms over south-
central Illinois that are expected to dissipate within the next
2-3 hours. Gusty winds have been reported with theses storms and
expect the heavy downpours at the cores of the storms will reduce
the visibility to IFR. There is also a subtle boundary showing up
on radar moving through the STL Metro area...just east of KSTL.
This boundary is drifting west and the environment is very
favorable for thunderstorms at this time. There is a chance that
another storm or cluster of storms could develop on this boundary
before 02Z, tho confidence is low at this time.

Expect visibility to drop locally to MVFR overnight, primarily in
river valleys. Some haze will likely persist after sunrise Sunday,
but VFR flight conditions are expected to prevail for most of the day.

Specifics for KSTL:

Expect VFR flight conditions to prevail at Lambert tonight. There
is a subtle boundary showing up just east of the terminal at this
time. This boundary is drifting west and the environment is very
favorable for thunderstorms. There is a chance that another storm
or cluster of storms could develop on this boundary before 02Z,
tho confidence is low at this time. Expect VFR flight conditions
and southwest flow to prevail at Lambert Sunday.



MO...HEAT ADVISORY until 7 PM CDT Monday FOR Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Shelby MO-St. Charles MO-St.
     Francois MO-Ste. Genevieve MO-Warren MO-Washington MO.

     EXCESSIVE HEAT WARNING until 7 PM CDT Monday FOR St. Louis City
     MO-St. Louis MO.

IL...HEAT ADVISORY until 7 PM CDT Monday FOR Adams IL-Bond IL-Brown
     IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Marion IL-Monroe IL-Montgomery IL-Pike IL-
     Randolph IL-Washington IL.

     EXCESSIVE HEAT WARNING until 7 PM CDT Monday FOR Madison IL-St.
     Clair IL.



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